I put one in my new boat (replacing a Webasto). The old Webasto was worth enough in parts ($75) to almost cover my new heater ($99 and exactly like the one in the first post). When shopping, look closely at what is included. The muffler is generally worthless as it isn't for enclosed spaces. The air ducts are generally too short. I bought an additional "kit" that had a Y connector instead of the T connector and more 75mm air ducting. These little heaters need every bit of help you can give them.
One of the extras that came with mine was a remote. Useful for me as I can turn on the heat from the V berth without getting out of bed. Decadent. Also check the thermostat provided. Some are quite simple. Others (once you figure them out) have as many settings as a fancy home thermostat. Go to YouTube to find out how to program them. Trying to decipher the instruction booklet is wasted time.
Some other accessories that may or may not come with the kit: You will need to buy an exhaust through-hull fitting and buy or make a muffler (if you want it to be silent). Webasto/Planar, etc. have these on their websites or you can get them unbranded and cheaper on Ebay. I haven't seen a cheap exhaust muffler, so I fabricated both of mine. Another item is a silencer for the combustion air intake. It is a surprisingly loud whine and, unlike the exhaust, is generally inboard. My Webasto was originally plumbed to take in both combustion air and circulation air from outside. I eliminated that with no bad effects. Shorter runs gives better performance. I went from an 11Kw Webasto to an 8Kw "Warmtoo" brand heater with no loss in performance. In fact, I added a register in the head for more even heating of the boat.
I just added a "smart" ammeter that shows constant charge and discharge of the batteries, including available Amp Hours left. The little heater uses a glow plug to ignite (@ 9 amps for 30 seconds). On high, the fan draws 3 amps, on low (most of the time) it draws 1. When shut off, it heats up the glow plug again, shuts off the fuel, and increases the burner fan speed. This is supposed to burn out any accumulated carbon from the heater running at low speeds for hours, which tends to be the biggest complaint on "old school" diesel heaters. So far, so good.